The invention is directed to a process for the pretreatment of light metal surfaces which are commonly coated with an oxide layer, especially aluminium, titanium, magnesium, beryllium and their alloys for the galvanic deposition of metallic coatings.
Light metals and light metal alloys without a pretreatment are practically impossible to galvanize since the oxide film which is always present on the light metal surface prevents the adhesion of the metallic coating is applied to the surface. Even if the oxide film is removed and the clean metal surface is free it immediately forms the oxide film again in the air or aqueous solutions. Therefore there have been numerous attempts to permanently remove this oxide layer or to increase it in order to anchor the metal coating in the pores of the oxide layer. The processes developed for permanent removal of the oxide layer in the practice are just as little completely satisfactory as the anchoring processes in the synthetically thickened oxide layer.
Therefore it was the problem of the present invention to develop the most universal process possible for pretreatment of oxide layer coated light metals before the galvanization (electroplating) in aqueous solution, which should be usable with all light metals especially for aluminum, magnesium, titanium, beryllium and their alloys, wherein the later electroplated layer must adhere well to the base.